Systems and methods for posterior dynamic stabilization of the spine

ABSTRACT

Devices, systems and methods for dynamically stabilizing the spine are provided. The devices include a radially expandable spacer having an undeployed configuration and a deployed configuration, wherein the spacer has axial and radial dimensions for positioning between the spinous processes of adjacent vertebrae. The systems include one or more spacers and a mechanical actuation means for delivering and deploying the spacer. The methods involve the implantation of one or more spacers within the interspinous space.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 11/052,002, filed on Feb. 4, 2005, which is acontinuation-in-part of U.S. patent application Ser. No. 11/006,502,filed on Dec. 6, 2004, which is a continuation-in-part of U.S. patentapplication Ser. No. 10/970,843, filed on Oct. 20, 2004, incorporatedherein by reference in their entireties.

FIELD OF THE INVENTION

The present invention is directed towards the treatment of spinaldisorders and pain. More particularly, the present invention is directedto systems and methods of treating the spine, which eliminate pain andenable spinal motion, which effectively mimics that of a normallyfunctioning spine.

BACKGROUND OF THE INVENTION

FIG. 1 illustrates a portion of the human spine having a superiorvertebra 2 and an inferior vertebra 4, with an intervertebral disc 6located in between the two vertebral bodies. The superior vertebra 2 hassuperior facet joints 8 a and 8 b, inferior facet joints 10 a and 10 b,and spinous process 18. Pedicles 3 a and 3 b interconnect the respectivesuperior facet joints 8 a, 8 b to the vertebral body 2. Extendinglaterally from superior facet joints 8 a, 8 b are transverse processes 7a and 7 b, respectively. Extending between each inferior facet joints 10a and 10 b and the spinous process 18 are laminal zones 5 a and 5 b,respectively. Similarly, inferior vertebra 4 has superior facet joints12 a and 12 b, superior pedicles 9 a and 9 b, transverse processes 11 aand 11 b, inferior facet joints 14 a and 14 b, laminal zones 15 a and 15b, and spinous process 22.

The superior vertebra with its inferior facets, the inferior vertebrawith its superior facet joints, the intervertebral disc, and sevenspinal ligaments (not shown) extending between the superior and inferiorvertebrae together comprise a spinal motion segment or functional spineunit. Each spinal motion segment enables motion along three orthogonalaxes, both in rotation and in translation. The various spinal motionsare illustrated in FIGS. 2A-2C. In particular, FIG. 2A illustratesflexion and extension motions and axial loading, FIG. 2B illustrateslateral bending motion and FIG. 2C illustrated axial rotational motion.A normally functioning spinal motion segment provides physiologicallimits and stiffness in each rotational and translational direction tocreate a stable and strong column structure to support physiologicalloads.

Traumatic, inflammatory, metabolic, synovial, neoplastic anddegenerative disorders of the spine can produce debilitating pain thatcan affect a spinal motion segment's ability to properly function. Thespecific location or source of spinal pain is most often an affectedintervertebral disc or facet joint. Often, a disorder in one location orspinal component can lead to eventual deterioration or disorder, andultimately, pain in the other.

Spine fusion (arthrodesis) is a procedure in which two or more adjacentvertebral bodies are fused together. It is one of the most commonapproaches to alleviating various types of spinal pain, particularlypain associated with one or more affected intervertebral discs. Whilespine fusion generally helps to eliminate certain types of pain, it hasbeen shown to decrease function by limiting the range of motion forpatients in flexion, extension, rotation and lateral bending.Furthermore, the fusion creates increased stresses on adjacent non-fusedmotion segments and accelerated degeneration of the motion segments.Additionally, pseudarthrosis (resulting from an incomplete orineffective fusion) may not provide the expected pain-relief for thepatient. Also, the device(s) used for fusion, whether artificial orbiological, may migrate out of the fusion site creating significant newproblems for the patient.

Various technologies and approaches have been developed to treat spinalpain without fusion in order to maintain or recreate the naturalbiomechanics of the spine. To this end, significant efforts are beingmade in the use of implantable artificial intervertebral discs.Artificial discs are intended to restore articulation between vertebralbodies so as to recreate the full range of motion normally allowed bythe elastic properties of the natural disc. Unfortunately, the currentlyavailable artificial discs do not adequately address all of themechanics of motion for the spinal column.

It has been found that the facet joints can also be a significant sourceof spinal disorders and debilitating pain. For example, a patient maysuffer from arthritic facet joints, severe facet joint tropism,otherwise deformed facet joints, facet joint injuries, etc. Thesedisorders lead to spinal stenosis, degenerative spondylolithesis, and/oristhmic spondylotlisthesis, pinching the nerves that extend between theaffected vertebrae.

Current interventions for the treatment of facet joint disorders havenot been found to provide completely successful results. Facetectomy(removal of the facet joints) may provide some pain relief; but as thefacet joints help to support axial, torsional, and shear loads that acton the spinal column in addition to providing a sliding articulation andmechanism for load transmission, their removal inhibits natural spinalfunction. Laminectomy (removal of the lamina, including the spinal archand the spinous process) may also provide pain relief associated withfacet joint disorders; however, the spine is made less stable andsubject to hypermobility. Problems with the facet joints can alsocomplicate treatments associated with other portions of the spine. Infact, contraindications for disc replacement include arthritic facetjoints, absent facet joints, severe facet joint tropism, or otherwisedeformed facet joints due to the inability of the artificial disc (whenused with compromised or missing facet joints) to properly restore thenatural biomechanics of the spinal motion segment.

While various attempts have been made at facet joint replacement, theyhave been inadequate. This is due to the fact that prosthetic facetjoints preserve existing bony structures and therefore do not addresspathologies that affect facet joints themselves. Certain facet jointprostheses, such as those disclosed in U.S. Pat. No. 6,132,464, areintended to be supported on the lamina or the posterior arch. As thelamina is a very complex and highly variable anatomical structure, it isvery difficult to design a prosthesis that provides reproduciblepositioning against the lamina to correctly locate the prosthetic facetjoints. In addition, when facet joint replacement involves completeremoval and replacement of the natural facet joint, as disclosed in U.S.Pat. No. 6,579,319, the prosthesis is unlikely to endure the loads andcycling experienced by the vertebra. Thus, the facet joint replacementmay be subject to long-term displacement. Furthermore, when facet jointdisorders are accompanied by disease or trauma to other structures of avertebra (such as the lamina, spinous process, and/or transverseprocesses) facet joint replacement is insufficient to treat theproblem(s).

Most recently, surgical-based technologies, referred to as “dynamicposterior stabilization,” have been developed to address spinal painresulting from more than one disorder, when more than one structure ofthe spine have been compromised. An objective of such technologies is toprovide the support of fusion-based implants while maximizing thenatural biomechanics of the spine. Dynamic posterior stabilizationsystems typically fall into one of two general categories: posteriorpedicle screw-based systems and interspinous spacers.

Examples of pedicle screw-based systems are disclosed in U.S. Pat. Nos.5,015,247, 5,484,437, 5,489,308, 5,609,636 and 5,658,337, 5,741,253,6,080,155, 6,096,038, 6,264,656 and 6,270,498. These types of systemsinvolve the use of screws that are positioned in the vertebral bodythrough the pedicle. Certain types of these pedicle screw-based systemsmay be used to augment compromised facet joints, while others requireremoval of the spinous process and/or the facet joints for implantation.One such system, the Zimmer Spine Dynesys® employs a cord which isextended between the pedicle screws and a fairly rigid spacer which ispassed over the cord and positioned between the screws. While thissystem is able to provide load sharing and restoration of disc height,because it is so rigid, it does not effective in preserving the naturalmotion of the spinal segment into which it is implanted. Other pediclescrew-based systems employ articulating joints between the pediclescrews. Because these types of systems require the use of pediclescrews, implantation of the systems are often more invasive to implantthan interspinous spacers.

Where the level of disability or pain to the affected spinal motionsegments is not that severe or where the condition, such as an injury,is not chronic, the use of interspinous spacers are preferred overpedicle based systems as they require a less invasive implantationapproach and less dissection of the surrounding tissue and ligaments.Examples of interspinous spacers are disclosed in U.S. Pat. Nos. Re.36,211, 5,645,599, 6,149,642, 6,500,178, 6,695,842, 6,716,245 and6,761,720. The spacers, which are made of either a hard or compliantmaterial, are placed in between adjacent spinous processes. The hardermaterial spacers are fixed in place by means of the opposing forcecaused by distracting the affected spinal segment and/or by use of keelsor screws that anchor into the spinous process. While slightly lessinvasive than the procedures required for implanting a pediclescrew-based dynamic stabilization system, implantation of hard or solidinterspinous spacers still requires dissection of muscle tissue and ofthe supraspinous and interspinous ligaments. Additionally, these tend tofacilitate spinal motion that is less analogous to the natural spinalmotion than do the more compliant and flexible interspinous spacers.Another advantage of the compliant/flexible interspinous spacers is theability to deliver them somewhat less invasively than those that are notcompliant or flexible; however, their compliancy makes them moresusceptible to displacement or migration over time. To obviate thisrisk, many of these spacers employ straps or the like that are wrappedaround the spinous processes of the vertebrae above and below the levelwhere the spacer is implanted. Of course, this requires some additionaltissue and ligament dissection superior and inferior to the implantsite, i.e., at least within the adjacent interspinous spaces.

With the limitations of current spine stabilization technologies, thereis clearly a need for an improved means and method for dynamic posteriorstabilization of the spine that address the drawbacks of prior devices.In particular, it would be highly beneficial to have a dynamicstabilization system that involves a minimally invasive implantationprocedure, where the extent of distraction between the affectedvertebrae is adjustable upon implantation and at a later time ifnecessary. It would be additionally advantageous if the system or devicewas also removable in a minimally invasive manner.

SUMMARY OF THE INVENTION

The present invention provides devices, systems and methods forstabilizing at least one spinal motion segment. The devices include anexpandable spacer or member having an unexpanded configuration and anexpanded configuration, wherein the expandable member in an expandedconfiguration has a size, volume and/or shape configured for positioningbetween the spinous processes of adjacent vertebrae in order to distractthe vertebrae relative to each other.

In certain embodiments, the expandable member is a balloon made ofeither non-compliant or compliant material which may be porous ornon-porous, or may include a mesh material which may be coated or linedwith a porous or non-porous material. The device may further include aport for coupling to a source of an inflation and/or expansion mediumfor inflating and/or expanding the expandable member. In certainembodiments, the port may be used to deflate or evacuate the expandablemember. The devices may further include one or more tabs for anchoringthe expandable member to the spinous processes. Optionally, the devicemay include one marker on a surface of the expandable member tofacilitate fluoroscopic imaging.

In other embodiments, the expandable members are cages, struts, wires orsolid objects having annular, spherical, cylindrical or ellipticalshapes when in an expanded condition. The expandable members may beself-expanding or adjustably expandable depending on the extent ofdistraction required.

The invention further includes systems for stabilizing at least onespinal motion segment which include one or more expandable members andan expansion medium for injection within or for filling the interior ofthe expandable member via the port. The subject systems may furtherinclude at least one means for anchoring or securing the expandablemember to the spinal motion segment.

The invention further includes methods for stabilizing at least onespinal motion segment which involve the implantation of one or moredevices or expandable spacers of the present invention, in which theexpandable member is positioned between the spinous processes ofadjacent vertebrae in an unexpanded or undeployed condition and thensubsequently expanded or deployed to a size and/or shape for selectivelydistracting the adjacent vertebrae. The invention also contemplates thetemporary implantation of the subject devices which may be subsequentlyremoved from the patient once the intended treatment is complete. Manyof the methods involve the percutaneous implantation of the subjectdevices from either an ipsolateral approach or a mid-line approach intothe interspinous space.

These and other objects, advantages, and features of the invention willbecome apparent to those persons skilled in the art upon reading thedetails of the invention as more fully described below.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is best understood from the following detailed descriptionwhen read in conjunction with the accompanying drawings. It isemphasized that, according to common practice, the various features ofthe drawings are not to-scale. On the contrary, the dimensions of thevarious features are arbitrarily expanded or reduced for clarity.Included in the drawings are the following figures:

FIG. 1 illustrated s perspective view of a portion of the human spinehaving two vertebral segments.

FIGS. 2A, 2B and 2C illustrate left side, dorsal and top views,respectively, of the spinal segments of FIG. 1A under going variousmotions.

FIG. 3A illustrates an interspinous device of the present invention inan unexpanded or collapsed state coupled to a cannula of the deliverysystem of the present invention. FIG. 3B is an enlarged view of theinterspinous device of FIG. 3A.

FIG. 4A illustrates an interspinous device of the present invention inan expanded state coupled to a cannula of the delivery system of thepresent invention. FIG. 4B is an enlarged view of the interspinousdevice of FIG. 4A.

FIGS. 5A-5C illustrates top, dorsal and side views of an initial step ofthe method of the present invention in which a cannula is delivered tothe target implant site.

FIGS. 6A and 6B illustrate dorsal and side views of the step ofdissecting an opening within the spinous ligament utilizing a cuttinginstrument of the system of FIGS. 3 and 4. FIG. 6C is an enlarged viewof the target area within the spinous ligament.

FIGS. 7A and 7B illustrate dorsal aid side views of the step ofinserting the interspinous device of FIG. 4A into the dissected openingof the spinous ligament. FIGS. 7C and 7D are enlarged views of thetarget area in FIGS. 7A and 7B, respectively.

FIGS. 8A and 8B illustrate dorsal aid side views of the step ofinflating or expanding the interspinous device of FIG. 4A within theimplant site; FIGS. 8C and 8D are enlarged views of the target area inFIGS. 8C and 8D, respectively.

FIG. 9A illustrates a side view of the step of filling the interspinousdevice of FIG. 4A with an expansion medium. FIG. 9B is an enlarged viewof the target area in FIG. 9A.

FIG. 10A illustrates a dorsal view of the step of further securing theinterspinous device of FIG. 4A within the implant site. FIG. 10B is anenlarged view of the target area in FIG. 10A.

FIGS. 11A and 11B illustrate dorsal aid side views of the step ofinserting another embodiment of an interspinous device into thedissected opening of the spinous ligament. FIGS. 11C and 11D areenlarged views of the target area in FIGS. 11A and 11B, respectively.

FIGS. 12A and 12B illustrate dorsal aid side views of the step ofexpanding the interspinous device of FIGS. 11A-11D within the implantsite. FIGS. 12C and 12D are enlarged views of the target area in FIGS.12A and 12B, respectively.

FIG. 13A illustrates a side view of the step of filling the interspinousdevice of FIGS. 11A-11D with an expansion medium. FIG. 13B is anenlarged view of the target area in FIG. 13A.

FIGS. 14A-14F illustrate dorsal views of another interspinous device ofthe present invention and a device for implanting the interspinousdevice where the implantation device is used initially distract theinterspinous space prior to implanting the interspinous device.

FIGS. 15A and 15B illustrate dorsal views of another interspinous deviceof the present invention implanted within an interspinous space.

FIGS. 16A and 16B illustrate dorsal views of another interspinous deviceof the present invention implanted within an interspinous space. FIG.16C is a side view of FIG. 16B.

FIGS. 17A and 17B illustrate side views of another interspinous deviceof the present invention implanted within an interspinous space. FIG.17C is a dorsal view of FIG. 17B.

FIGS. 18A and 18B illustrate another interspinous device of the presentinvention in undeployed and deployed states, respectively.

FIGS. 19A and 19B illustrate the device of FIG. 18 implanted within aninterspinous space and operably coupled to a delivery device of thepresent invention.

FIGS. 20A and 20B illustrate cut-away views of two embodiments of thehandle portion of the delivery device of FIGS. 19A and 19B.

FIG. 21 illustrates a cut-away view of a distal portion of the device ofFIG. 18 operably positioned over the delivery device of FIG. 20B.

FIGS. 22A-22C illustrate another interspinous spacer device of thepresent invention in undeployed, partially deployed and fully deployedstates, respectively.

FIGS. 23A-23C illustrate another interspinous spacer device of thepresent invention in undeployed, partially deployed and fully deployedstates, respectively.

FIGS. 24A-24C illustrate yet another interspinous spacer device of thepresent invention in undeployed, partially deployed and fully deployedstates, respectively.

FIGS. 25A-25C illustrate another interspinous spacer device of thepresent invention in undeployed, partially deployed and fully deployedstates, respectively.

FIGS. 26A and 26B illustrate perspective and front views of anotherinterspinous spacer device of the present invention in a deployed state.

FIG. 27 illustrates a front view of another interspinous spacer deviceof the present invention.

FIG. 28A illustrates a step in a method of implanting the interspinousspacer device of FIGS. 26A and 26B. FIGS. 28A′ and 28A″ illustrate sideand front views of the interspinous spacer device in an undeployed statein the context of the step illustrated in FIG. 28A.

FIG. 28B illustrates a step in a method of implanting the interspinousspacer device of FIGS. 26A and 26B. FIGS. 28B′ and 28B″ illustrate sideand front views of the interspinous spacer device in a partiallydeployed state in the context of the step illustrated in FIG. 28B.

FIG. 28C illustrates a step in a method of implanting the interspinousspacer device of FIGS. 26A and 26B. FIGS. 28C′ and 28C″ illustrate sideand front views of the interspinous spacer device in a partiallydeployed state in the context of the step illustrated in FIG. 28C.

FIG. 28D illustrates a step in a method of implanting the interspinousspacer device of FIGS. 26A and 26B in which the spacer is fully deployedand being released from a delivery device.

FIG. 28E illustrates the interspinous spacer device of FIGS. 26A and 26Boperatively implanted within an interspinous space.

FIGS. 29A and 29A′ illustrate perspective and front views of anotherinterspinous spacer device of the present invention in an undeployedstate.

FIGS. 29B and 29B′ illustrate perspective and front views of theinterspinous spacer device of FIG. 29A in a partially deployed state.

FIGS. 29C and 29C′ illustrate perspective and front views of theinterspinous spacer device of FIG. 29A in a partially deployed state butone which is more deployed than depicted in FIG. 29B.

FIGS. 29D and 29D′ illustrate perspective and front views of theinterspinous spacer device of FIG. 29A in a fully deployed state.

FIGS. 30A and 30A′ illustrate perspective and front views of anotherinterspinous spacer device of the present invention in a fully deployedstate.

FIGS. 30B and 30B′ illustrate perspective and side views of theinterspinous spacer device of FIG. 30A in an undeployed state.

FIGS. 30C and 30C′ illustrate perspective and side views of theinterspinous spacer device of FIG. 30A in a partially deployed state.

DETAILED DESCRIPTION OF THE INVENTION

Before the subject devices, systems and methods are described, it is tobe understood that this invention is not limited to particularembodiments described, as such may, of course, vary. It is also to beunderstood that the terminology used herein is for the purpose ofdescribing particular embodiments only, and is not intended to belimiting, since the scope of the present invention will be limited onlyby the appended claims.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs.

It must be noted that as used herein and in the appended claims, thesingular forms “a”, “an”, and “the” include plural referents unless thecontext clearly dictates otherwise. Thus, for example, reference to “aspinal segment” may include a plurality of such spinal segments andreference to “the screw” includes reference to one or more screw andequivalents thereof known to those skilled in the art, and so forth.

Where a range of values is provided, it is understood that eachintervening value, to the tenth of the unit of the lower limit unlessthe context clearly dictates otherwise, between the upper and lowerlimits of that range is also specifically disclosed. Each smaller rangebetween any stated value or intervening value in a stated range and anyother stated or intervening value in that stated range is encompassedwithin the invention. The upper and lower limits of these smaller rangesmay independently be included or excluded in the range, and each rangewhere either, neither or both limits are included in the smaller rangesis also encompassed within the invention, subject to any specificallyexcluded limit in the stated range. Where the stated range includes oneor both of the limits, ranges excluding either or both of those includedlimits are also included in the invention.

All publications mentioned herein are incorporated herein by referenceto disclose and describe the methods and/or materials in connection withwhich the publications are cited. The publications discussed herein areprovided solely for their disclosure prior to the filing date of thepresent application. Nothing herein is to be construed as an admissionthat the present invention is not entitled to antedate such publicationby virtue of prior invention. Further, the dates of publication providedmay be different from the actual publication dates which may need to beindependently confirmed.

The present invention will now be described in greater detail by way ofthe following description of exemplary embodiments and variations of thedevices and methods of the present invention. The invention generallyincludes an interspinous spacer device as well as instruments for thepercutaneous implantation of the interspinous spacer. A key feature ofthe interspinous spacer device is that it is expandable from a lowprofile configuration to a higher profile or operative configuration.This design allows the device, when in the low profile condition, to bedelivered by percutaneous means without requiring the removal of anyportion of the spinal motion segment into which the device is implanted.

Referring now to the drawings and to FIGS. 3 and 4 in particular, anexemplary interspinous spacer device 24 of the present invention isillustrated in collapsed and expanded configurations, respectively.Interspinous device 24 includes an expandable spacer body 34 that has asize and shape when in the expanded condition for operative positioningbetween the spinous processes of adjacent superior and inferiorvertebrae of the spinal motion segment being treated. Expandable body 34is made of an expandable or inflatable biocompatible material such asnon-porous material, e.g., latex, acrylate or a metal mesh, e.g., anitinol or titanium cage.

Those spacers made of an inflatable non-porous material, i.e., balloontype spacers (see FIGS. 3-10), are inflated with an inflation orexpansion medium, such as air, saline, another biologically compatiblefluid, or a flowable solid material, such as polyurethane, or a gel,which thickens or hardens substantially upon injection into balloon 34.In one embodiment, balloon 34 is initially inflated with air to providesome structure or rigidity to it to facilitate its optimum positioningand alignment between the spinous processes. Once positioned as desired,balloon 34 is injected with a flowable solid material (the air thereinbeing displaced possibly via a vent hole within port 32). In certainembodiments, the expandable body is made of a non-compliant orsemi-compliant material so as to maintain a substantially fixed shape orconfiguration and ensure proper, long-term retention within the implantsite. In other embodiments, the expandable member may be made of acompliant material. In any embodiment, the compressibility andflexibility of balloon 34 can be selected to address the indicationsbeing treated.

Other embodiments of the subject spacers are made of an expandable meshor cage (see FIGS. 11-12). The mesh or cage maybe made of asuper-elastic memory material which is compressible for delivery througha cannula and which is self-expanding upon implantation. Upon expansion,the mesh or cage may be self-retaining whereby its struts, links orwires are sufficiently rigid by themselves to maintain the expandedcondition and withstand the natural forces exerted on it by spine. Themesh or cage may have an exterior coating or an interior lining made ofmaterials similar to or the same as that used for the balloon spacers,or may otherwise be embedded in such material. In certain embodiments,an expansion medium may be used to fill the interior of the cage or meshstructure, such as with a biologically compatible fluid or flowablesolid material used with the balloon-type embodiments.

In certain embodiments of present invention, either during the implantprocedure or in a subsequent procedure, the size or volume of theimplanted expandable spacer may be selectively adjusted or varied. Forexample, after an initial assessment upon implant, it may be necessaryto adjust, either reduce or increase, the size or volume of the spacerto optimize the intended treatment. Further, it may be intended to onlytemporarily implant the spacer for the purpose of treating a temporarycondition, e.g., an injured or bulging or herniated disk. Once therepair is achieved or the treatment completed, the spacer may beremoved, either with or without substantially reducing the size orvolume of the spacer. In other embodiments, the spacer as well as theinflation/expansion material may be made of biodegradable materialswherein the spacer degrades after a time in which the injury is healedor the treatment completed.

When unexpanded or deflated, as shown in FIGS. 3A and 3B (balloon type)and in FIGS. 11C and 11D (mesh type) expandable body 34 has a lowprofile, such as a narrow, elongated shape, to be easily translatedthrough a delivery cannula 70. The shape of expandable body 34, when inan expanded or inflated state, has larger profile which is generallyH-shaped. Expandable body 34 has lateral or side portions 30, endportions 26 and apexes 28 defined between the side portions 30 and theend portions 26. End portions 26 are preferably recessed or contoured toprovide a narrowed central portion along the height dimension or majoraxis of expandable body 34 to readily fit between and to conform to thespinous processes. Accordingly, expandable body 34 has an apex-to-apexdimension (i.e., height or major axis dimension) from about 3 to about 5cm and a width dimension (minor axis dimension) from about 2 to about 4cm

For those embodiments of expandable bodies which comprise a balloonconfiguration, balloon 34 has an inflation or injection port 32 at asidewall 30 for coupling to a source of inflation or expansion materialor medium. Port 32 may consist of a one-way valve which is self-sealingupon release from an inflation mechanism or tube 76. Port 32 is furtherconfigured to releasably engage from tube 76, where such engagement maybe threaded or involve a releasable locking mechanism. Where theexpandable body comprises a mesh or cage, port 32 simply acts as an exitport, however, where an expansion material is used, it also functions asan injection port for the expansion material.

Optionally, device 24 may include a pair of tabs 36 which may bepositioned on one side of the device where the tabs 36 are preferablysituated at the apexes 28 of expandable body 34. Pins or screws (not yetshown) may be used to secure the tabs against the spinous process tofurther ensure long-term retention of device 24 within the implant site.Tabs 36 are made of a biocompatible material, such as latex, acrylate,rubber, or a metal, and may be made of the same material used for theexpandable member 34. Shown here attached to tabs 36 are tethers 38which are used in part to manipulate the positioning of expandable body34 upon implantation into the targeted spinal motion segment. Thetethers may be made of any suitable material including but not limitedto materials used to make conventional sutures. They may also be made ofa biodegradable material. While two tabs and associated tethers areprovided in the illustrated embodiment, one, three or more may beemployed, where the respective tabs are located on the expandable bodyso as to be adjacent a bony structure of the vertebra suitable foranchoring thereto. In embodiments which do not employ securing tabs 36,tethers 38 may be attached directly to the expandable body itself.

Optionally still, device 24 may further include radiopaque markers 40 onthe surface of expandable body 34 visible under fluoroscopic imaging tofacilitate positioning of the expandable body. Any number of markers 40may be employed anywhere on expandable body 34, however, as few as fourmarkers, one at each apex, may be sufficient. With embodiments employingcage or mesh expandable bodies, the cage or mesh material itself may beradiopaque.

A system of the present invention includes a cannula device 70 having anouter sheath 72, a proximal hub 78 and preferably at least two interiorlumens 74, 76 for the percutaneous delivery of the device and othertools for implanting the device, which tools may include a cuttinginstrument 60 (see FIG. 6C), a device delivery instrument 77, anendoscope, etc., which tools will be further discussed in the context ofthe description of the subject methods with reference to FIGS. 5-10.

In FIGS. 5A-5C, the spinal motion segment of FIG. 1 is illustratedhaving spinal ligament 54 extending between the superior spinous process18 and the inferior spinous process 22. A percutaenous puncture is madeinto the skin 30 adjacent the target spinal motion segment of a patientundergoing the implantation of the interspinous device of the presentinvention, and a cannula 70 is penetrated to the spinous ligament 54.The puncture and subsequent penetration may be made by way of a sharpdistal tip of cannula 70 or by a trocar (not shown) delivered through alumen of cannula 70.

As illustrated in FIGS. 6A-6C, the spinous ligament 54 is then dissectedand an opening 58 created therein by way of a cutting instrument 60,such as a simple scalpel, an electrosurgical device or the like,delivered through a lumen of cannula 70. Cutting instrument 60 may thenbe removed from cannula 70 and, as illustrated in FIGS. 7A-7D (balloontype) and in FIGS. 11A-11D (cage type), a delivery instrument 16 havinginterspinous device 24 operatively preloaded is delivered throughcannula 70.

The preloading of device 24 to delivery instrument 76 involves providingexpandable body 34 in an unexpanded or deflated state and releasablycoupled, as described above, by way of inflation or injection port 32 ofexpandable body 34 to the distal end of delivery instrument 76. Inaddition to functioning as a pusher, instrument 76 may act as aninflation lumen for balloon type embodiments through which an inflationmedium is transported to within expandable body 34.

Depending upon the material used to fabricate expandable body 34, theexpandable body may have a degree of stiffness in an unexpanded ordeflated state such that it may maintain an elongated configuration soas to be directly insertable and pushable through cannula 70. This maybe the case where the expandable member 34 is made of a cage or meshmaterial. Alternatively, a pusher or small diameter rod (not shown) maybe inserted through inflation port 32 to within expandable body 34 tokeep it in an elongated state so as to prevent expandable body 34 frombunching within cannula 70 and to provide some rigidity to moreeffectively position the expandable body in the target implant site. Therod is then removed from expandable body 34 and from delivery device 76upon positioning the expandable body at the target implant site. Ineither case, expandable body 34 is folded or compressed about its minoraxis with the side wall opposite the inflation port 32 defining a distalend 25 (see FIG. 3B) and the apexes 28 of the expandable body foldedproximally of distal end 25 to provide a streamline, low profileconfiguration for delivery through cannula 70.

Once interspinous device 24 is preloaded to delivery device 76 as justdescribed, device 24 is then inserted into a lumen of cannula 70 withtethers 38 pulled back and trail proximally so that the tether ends 38 aextend from hub 78 of cannula 70. Expandable body member 34 istranslated through cannula 70 to within opening 58 within spinousligament 54 as best illustrated in FIGS. 7C and 11C. For best results,expandable body 34 is centrally positioned within opening 58 so that thecountered ends 26 of expandable body 34 readily engage with the opposedspinous processes 18, 22. Fluoroscopy may be employed to visualizemarkers 40 so as to ensure that expandable body 34 centrally straddlesthe spinous ligament opening 58, i.e., the markers on the distal side 25of the expandable body are positioned on one side of the spine and themarkers on the proximal side of the expandable body (the side on whichport 32 is located) are positioned on the other side of the spine.

Once centrally positioned, expandable body 34 is inflated or expanded,as illustrated in FIGS. 8A-8D and 12A-12D. For balloon spacers,inflation occurs by allowing an inflation or expansion medium, asdiscussed above, to enter into the interior of the expandable body viaport 32. For expandable mesh spacers, the expandable body may beconfigured to expand automatically upon exiting cannula 70. Theinflation or expansion of expandable body 34 may also be visualizedunder fluoroscopy whereby markers 40, as best shown in FIG. 8C, areobserved and the position of expandable body 34 may be adjusted toensure optimum positioning upon complete inflation. Adjustments of theexpandable body's position may be accomplished by manually pulling onone or both tether ends 38 a which in turn pulls on tabs 36 to which thetethers 38 are attached at their proximal ends. The tethers 38 areselectively pulled as necessary to center or optimally positioninterspinous expandable body 34 to achieve the desired treatment of thetargeted spinal motion segment.

With embodiments in which the expandable body is initially inflated withair and then filled with a solid or fluid medium, the latter ispreferably not delivered or injected into the interior of the expandablebody until the position of the expandable body within the interspinousspace has been verified and optimized. This is beneficial in situationswhere, upon inflation, it is found that the expandable body ismisaligned within the interspinous space and requires repositioning. Theexpandable body may simply be deflated of air to the extent necessaryand repositioned in a less inflated or deflated state. If necessary, forexample where it is found that the maximum spacer or expandable bodysize is insufficient for the particular application at hand, expandablebody 34 may be completely deflated and removed and replaced with a moresuitably sized unit.

For balloon spacers and those mesh spacers which are not by themselvessufficiently self-retaining, once the position and extent of inflationor expansion of expandable body 34 are optimized, the expansion medium,e.g., polyurethane, is allowed to flow or injected into the interior ofthe expandable body via port 32. As illustrated in FIGS. 9A and 9B,expandable body 34 is caused to expand to a selected volume and in sodoing forces apart (see arrow 80) the spinous processes 18, 22 inbetween which it is situated. This selective distraction of the spinousprocesses also results in distraction of the vertebral bodies 2, 4 (seearrow 82) which in turn allows the disk, if bulging or distended, toretract to a more natural position (see arrow 84). Again, the extent ofdistraction or lordosis undergone by the subject vertebrae can bemonitored by observing expandable body markers 40 under fluoroscopy.

The extent of possible distraction maybe limited by the capacity ofexpandable body 34 and the type of expandable body material employed. Incertain embodiments, such as expandable bodies made of non-compliant orsemi-compliant balloons, the requisite volume of the inflation mediummay be substantially fixed whereby the balloon achieves its fullyexpanded configuration upon filling it with the fixed volume of medium.In other embodiments, such as with balloons made of a compliantmaterial, the extent of expansion may be variable and selectableintraoperatively depending on the extent of lordosis or distraction tobe achieved between the spinous processes in which balloon 34 is nowinterposed.

Upon achieving the desired distraction between the vertebrae,inflation/expansion lumen 76 is disengaged from expandable body port 32which then becomes sealed by means of a one-way valve that is closedupon disengagement of lumen 76. Inflation/expansion lumen is thenremoved from cannula 70. While the opposing compressive force exerted onexpandable body 34 by the distracted spinous processes 18, 22 may besufficient to permanently retain expandable body 34 therebetween, theinterspinous device may be further secured to the spinous processes 18,22 to ensure that the expandable body does not slip or migrate from itsimplanted position. To this end, tabs 36 are anchored to the spinousprocesses as illustrated in FIGS. 10A and 10B and in FIGS. 13A and 13B.Any type of anchoring means, such as screws, tacks, staples, adhesive,etc. may be employed to anchor tabs 36. Here, cannulated screws 90 areused as anchors and are delivered to the target site releasably coupledto screw driving instrument 88. While various screw attachment andrelease mechanisms may be employed, a simple configuration involvesproviding the screws 90 with a threaded inner lumen which is threadablyengagable with the threaded distal end of instrument 88.

To ensure accurate placement of screws 90, along with instrument 88, canbe tracked and translated over respective tethers 38, which function asguide wires. By manipulating instrument 88, the screws are driven orscrewed into the respective spinous process. Screwdriver 88 is thendisengaged or unscrewed from screw 90. After both tabs 36 are securelyanchored to the spinous processes, the screwdriver and the cannula maybe removed from the patient's back.

FIGS. 14A-14F illustrate an alternative method for implanting theexpandable member. In particular, the method contemplates pre-inflatingor pre-expanding the expandable member prior to positioning theexpandable member within the interspinous space. To accomplish this, thevertebrae 2 and 4 may be distracted prior to insertion of thepre-expandable balloon implant. A temporary distraction mechanism, suchas another balloon or a mechanically actuated device, is inserted intothe interspinous space. When the desired amount of distraction isachieved, the permanent or implantable expandable member can then beplaced within the interspinous space, and the temporary distractionmember may then be removed from the space.

While certain of the expandable spacers are intended to be permanentlyimplanted within a spine, certain others may be implanted onlytemporarily to facilitate the healing of an injury or the treatment of areversible or non-chronic condition, such as a herniated disk. For suchtemporary treatments, the expansion material most likely is a fluid,such as saline, which may be easily aspirated through port 32 or may beallowed to drain out via a penetration or cut made in the expandablemember. In those embodiments in which the expansion material is aflowable solid, which may or may not subsequently harden within theexpandable member, the material may be one that is reconstitutable intoa liquid form which may then be subsequently aspirated or evacuated fromthe expandable member. For percutaneous removal of the expandablemember, a cannula such as cannula 70 may be used and an aspirationinstrument delivered therethrough and coupled to port 32. Afterdeflation and/or evacuation of the expandable member, and removal of thetacks, sutures, staples, etc. if such are used to secure tabs 36, theexpandable member may be easily removed through cannula 70. Withbiodegradable spacers, removal of the spacer is obviated.

It should be noted that any of the above-described steps or procedures,including but not limited to cannulation of the target area, dissectionof the spinous ligament, insertion of the expandable body within thedissected opening of the spinous ligament, inflation and/or expansion ofthe expandable body, adjustment or readjustment of the expandable body,and anchoring of the tabs, etc., may be facilitated by way of a scope 62delivered through a lumen of cannula 70 to the open distal tip ofcannula 70. Alternatively, a second cannula delivered through anotherpercutaneous penetration may be employed for use of an endoscope and anyother instruments needed to facilitate the procedure.

FIG. 14A illustrates an exemplary embodiment of a temporary distractionmechanism 100 having an expandable strut configuration. Mechanism 100includes bilateral struts 102 which are hinged and foldable at hubs 104,respectively. Bridging the struts 102 at superior and inferior ends arespinous process engagement portions 106 which are preferably configuredto conformingly engage with the spinous processes 18, 22. Extendingcentrally between hubs 104 is a distal portion of guide wire 108, whichalso extends proximally through proximal hub 104 a. Guide wire 108 is inthreaded engagement with both hub 104 a whereby hub 104 a can betranslated both proximally and distally along guide wire 108. As such,expandable member 100 can be provided in a low profile, compressed stateupon proximally translating hub 104 a in a proximal direction. In such alow-profile state, distraction mechanism 100 is easily deliverablethrough cannula 70, as described above, to with the interspinous space.Upon proper positioning, distraction mechanism 100 is expandable to ahigher profile or expanded state by translating hub 104 a toward hub 104b in a distal direction along guide wire 108, as illustrated in FIG.14A.

After the desired amount of distraction is achieved between vertebrae 2and 4, an implantable expandable member 110 of the present invention isdelivered adjacent the distracted spinal motion segment. Expandablemember 110 may be delivered from the same incision and side asdistraction mechanism 100 (ipsolateral approach) and as well as throughthe same working channel, or may be delivered through a differentincision on the same or opposing side of the spinal motion segment beingtreated (bilateral approach) using two different working channels. Inthe illustrated embodiment, expandable member 110 is delivered from thesame side of the spinous process as distraction mechanism 100.Expandable member 110 may delivered through a separate designated lumenin cannula 70 and translated distally of hub 104 b of distractionmechanism 100.

As shown in FIG. 14B, after deployment, expandable member 110 isinflated or expanded as described above with respect to expandablemember 34, for example, by way of an inflation lumen extending throughguide wire 108. Tethers 112 may be provided on expandable member 110 toretract and manipulate it to within the interspinous space, asillustrated in FIG. 14C. Once expandable member 110 is properlypositioned within the interspinous space, distraction mechanism 100 maybe removed from the interspinous space immediately or, if the expandablemember has been filled with a curable expansion medium or one thatinvolves setting or hardening, the distraction mechanism may be kept inthe interspinous space until the desired consistency, curing orhardening has been achieved by the expansion medium. To removedistraction mechanism 100 from the interspinous space, its profile isreduced to a low profile state, as illustrated in FIG. 14D. As mentionedearlier, this is accomplished by translating proximal hub 104 aproximally along guide wire 108. Distraction member 100 may be retractedout through a cannula or removed directly in this low profile state,leaving expandable member 100 alone within the implant site asillustrated in FIG. 14E. Tethers 112 may then be cut or secured inplace. Optionally, a strap 116 or the like may be implanted to furthersecure expandable member 110 within the implant site and reduce the riskof migration. Here, bores or holes 114 have been formed through thethickness of the spinous processes 18, 22 and strap 116 threaded therethrough with its ends secured together by a securing means 120, such asa suture, staple or clip, as illustrated in FIG. 14F. Alternatively,strap 116 could be wrapped around the spinous processes 18, 22.

In addition to the expandable balloon spacers, the present inventionfurther provides for mechanically expandable spacers such as thoseillustrated in FIGS. 15-17. For example, expandable spacer 130 of FIG.15A is a cage-like structure having spaced-apart, parallel strut members132 extending between and fixed to hubs 134. Like the distractionmechanism of FIGS. 14A-14F, spacer 130 may be provided on anddeliverable by way of a guide wire 136 which is threadably engaged toand disengagable from proximal hub 134 a. After placement of spacer 130within the interspinous space, as illustrated in FIG. 15A, spacer 130 isexpanded by advancing proximal hub 134 a distally along guide wire 136thereby forcing struts 132 radially outward and away from each otherwhereby the expanded configuration of spacer 130 is elliptical or, in amore advanced state of expansion, substantially spherical. Once thedesired degree of distraction is achieved between vertebrae 2 and 4,guide wire 136 unthreaded from hub 134 a and removed from the implantregion.

FIGS. 16A and 16B illustrate another embodiment of an expandable spacer140 which is in the form of a coiled band 142 terminating at an outerend 144 having a configuration for receiving and locking onto inner end146 upon full expansion or unwinding of the coil. The diameter of coil142 in an unexpanded or fully wound state is small enough to allow easyinsertion between spinous processes 18, 22. Upon proper positioningwithin the interspinous space, coil 142 is allowed to expand and unwindthereby distracting vertebrae 2 and 4 apart from each other. Once thedesire level of distraction is achieved, inner end 146 is coupled toouter end 144. While the figures show band 142 inserted transversely tospinous processes 18, 22, it may alternatively be inserted in line or inthe same plan defined by the spinous processes.

FIGS. 17A-17C illustrate another interspinous spacer 150 havinginterlocked nested portions 152. Nested portions 152 are each shaped andconfigured to be received within one of its adjacent portions and toreceive the other of the adjacent portions when in a low profile state,as illustrated in FIG. 17A. Upon expansion of spacer 150, which may bespring loaded or be expandable by way of an instrument (not shown) whichmay be inserted into the spacer's center and rotated to flare portions152, vertebrae 2 and 4 are caused to distract from each other. Portions152 may have a configuration or shape which allow them to bite or diginto the spinous process 18, 22 and become securely retained therein.

FIGS. 18A and 18B illustrate another interspinous spacer 160 of thepresent invention in an undeployed or unexpanded state and a deployed orexpanded state, respectively. Spacer 160 includes an expandable tubularmember 162 having end portions 164 a, 164 b which are capped by hubs 166a, 166 b, respectively. As is explained in greater detail below, one orboth hubs may be provided fixed to tubular member 162 or may bereleasably coupled thereto. A sleeve or retaining member 168 iscircumferentially positioned about tubular between end portions 164 a,165 a. Most typically, retaining member 168 is positioned substantiallycentrally (as shown) on tubular member 162, but may be positionedlaterally towards one or the other end. Retaining member 168 has alength that covers about one third of the length of tubular member 162,but may be longer or shorter depending on the application. As isexplained in greater detail below, interspinous spacer 160 may furtherinclude a core member (shown in FIG. 21) within the lumen of the tubularmember and which may be provided integrated with spacer 160.Alternatively, the core member may be provided as a detachable componentof the device used to deliver and implant the spacer (see FIGS. 19A and19B).

In the undeployed state, as illustrated in FIG. 18A, spacer 160 has anelongated tubular or cylindrical shape, and may have any suitablecross-sectional shape, e.g., circular, oval, starred, etc., where themore angular cross-sections may allow the device to bite or dig into thespinous processes and for better retention. In this undeployed orlengthened state, tubular member 162 has a length in the range fromabout 20 mm to about 80 mm, and more typically from about 30 mm to about50 mm, and a diameter or average thickness in the range from about 4 mmto about 12 mm, and more typically from about 6 mm to about 9 mm. Assuch, spacer 160 is deliverable to an implant site between adjacentspinous processes in a minimally invasive manner.

In the deployed state, as illustrated in FIG. 18B, spacer 160 has adumbbell or H-shaped configuration, where the length of spacer 160 isless than and the diameter or height of spacer 160 is greater than thecorresponding dimensions of the spacer when in an undeployed state. Inparticular, the length dimension of the end portions 164 a, 164 b oftubular member 162 has been reduced by about 25% to about 70% while thediameter of the end portions 164 a, 164 b has been increased by about50% to about 600%, and the diameter of the central or sleeve-coveredportion has been increased by about 200% to about 400%, where thediameter of the portions of the tubular member 164 a, 164 b not coveredby retaining member 168 have a greater diameter than the portion oftubular member 162 which is covered by retaining member 168. Theincreased diameter of covered or central portion 168 distracts theadjacent vertebrae so as to provide pain relief. The diameter of hubs166 a, 166 b may remain constant upon deployment of device 160. In thisdeployed state, tubular member 162 has a length in the range from about15 mm to about 50 mm, and more typically from about 20 mm to about 40mm, and an end portion diameter in the range from about 10 mm to about60 mm, and more typically from about 15 mm to about 30 mm, and a centralportion diameter in the range from about 5 mm to about 30 mm, and moretypically from about 8 mm to about 15 mm. As such, when operativelyplaced and deployed within an interspinous space, the deployed spacer160 fits snugly within the interspinous space and is held in place bythe surrounding muscle, ligaments and tissue.

Any suitable materials may be used to provide a spacer 160 which isprovided in a first state or configuration, e.g., the undeployed stateillustrated in FIG. 18A, and which can be manipulated to achieve asecond state or configuration, and back again if so desired. A polymerbased material or any other material which allows for simultaneous axialshortening and radial expansion is suitable for use to form tubularmember 162. The end portions 164 a, 164 b may be made of the same or adifferent material as that of the central or covered portion. A flexibleor shaped memory material or any other material which also allows forsimultaneous axial shortening and radial expansion, but which is lessexpandable, i.e., maintains a compressive force about tubular member162, than the material employed for tubular member 162 may be used toform retaining member 168. As such, retaining member 168 limits theextent of radial expansion as well as axial shortening that the coveredportion of tubular member 162 can undergo. Examples of suitablematerials for the retaining member include but are not limited toNitinol or polyethelene in a braided or mesh form. Further, theconstruct of retaining member 168 may be such that the radial forceapplied to the portion of tubular member 162 that it covers is constantor consistent along its length so as to maintain a constant diameteralong its length or, alternatively, may have a varying radial force soas to allow for selective shaping of the covered portion of tubularmember when in a deployed state. Retaining member 168 may be constructedso as to resist bending or flexing upon forcible contact with thespinous processes and, as such, does not conform to the spinousprocesses. Conversely, the retaining member 168 may be constructed froma more flexible material that allows for some compression and, as such,may conform or be conformable to the spinous processes. Further, thephysical properties and dimensions of the materials used for both thetubular member and the retaining may be selected to provide the desiredamount of distraction between target vertebrae.

Referring now to FIGS. 19A and 19B, spacer 160 is shown operativelyemployed within an interspinous space and coupled to delivery device170. Delivery device 170 includes an outer shaft 172 and an inner shaft178, movable relative (axially, rotationally or both) to outer shaft172, both extending from a handle mechanism 174. For example, innershaft 178 may be configured to be retracted proximally within outershaft 172, or outer shaft 172 may be configured to be advanced distallyover inner shaft 178, or both configurations may be employed together,i.e., while outer shaft 178 is advanced, inner shaft 178 is retracted.The relative movement may be accomplished in any suitable manner, forexample by way of a screw configuration, i.e., where the shaft membersengage by way of corresponding threads, as illustrated in FIG. 20A, orby way of a ratchet configuration, as illustrated in FIG. 20B. Therelative movement is accomplished by manual actuation of actuator 176coupled to handle 174. While only mechanical embodiments of the movementactuation are illustrated, the same can be achieved by electrically orpneumatically-driven devices or mechanisms.

As mentioned above, spacer 160 may be provided with an integrated coremember or the core member may be detachably provided on the distal end182 of inner shaft 178. In the first embodiment, distal end 182 of innershaft 178 is configured to temporarily couple with a proximal end (i.e.,the end closest to handle 174) of the core member. In the latterembodiment, the distal end 182 of inner shaft 178 is configured to beinserted into the lumen of tubular member 162, as illustrated in FIG.21, connect to or engaged with distal hub 166 b (i.e., the hubpositioned furthest from handle 174) and be detachable at a proximal end184 from inner shaft 178 to function as a core member. An advantage ofthe latter embodiment is that the end portion 182 of the inner shaft 178functioning as the core member may have a length that is as short as thelength of tubular member 172 when in a deployed state, with no extralength or remaining portion extending laterally of the implanted device.In the integrated embodiment, the core length may need to be as long astubular member 172 when in the undeployed state. However, the coremember may be segmented to allow for selective removal of one or morelengths or portions from the proximal side of the core member subsequentto implantation of the spacer so as not to have any excess lengthextending from the spacer.

With either embodiment, retraction of inner shaft 178, as describedabove, retracts distal hub 166 b towards proximal hub 166 a and/oradvancement of outer shaft 172 advances proximal hub 166 a towardsdistal hub 166 b, thereby causing tubular member 162 to be compressedaxially, and thus expanded radially, as shown in FIG. 19B. While distalhub 166 b may be fixed to tubular member 162, proximal hub 166 a may beprovided as a separate component having a central bore which allows itto receive and axially translate over inner shaft 178. Proximal hub 166a may be configured to readily slide over inner shaft 178 in a distaldirection (but possibly not in a proximal direction) or may be threadedin order to advance over inner shaft 178. The advancement of proximalhub 166 a axially compresses tubular member 172 and causes it toradially expand. The axial compression or radial expansion may becontinued until the desired extent of distraction occurs betweenvertebrae 2 and 4. When the desired level of distraction is achieved,proximal hub 166 a is secured to either the proximal end of tubularmember 162 and/or the proximal end of the core member 182, such as by athreaded or snap-fit engagement or by activating a lock mechanism (notshown). Inner shaft 178 may then be released from the core member (ordistal end 182 of inner shaft 178 may be released from inner shaft 178and left within tubular member 172 to function as the core member)which, along with the end hubs 166 a and 166 b, maintain the implantedspacer 160 in a deployed state so as to maintain distraction between thevertebrae.

The reconfiguration of spacer 160 may be further facilitated byselectively configuring the wall of tubular member 162. For example, theinterior or luminal surface of tubular member 162 may be contoured orincorporated with divets or spaces 180 where, upon compression oftubular member 162, the walls of the uncovered portions 164 a, 164 b oftubular member 162 will more readily fold inward to provide theresulting configuration shown in FIG. 18B.

FIGS. 22A-22C illustrate another interspinous spacer 190 of the presentinvention in an undeployed/unexpanded state, in an intermediate stateduring deployment and in a deployed/expanded state, respectively. Spacer190 includes expandable end portions 192 a, 192 b which are capped byhubs 198 a, 198 b, respectively. As mentioned previously, one or bothhubs may be provided fixed to the end members or may be releasablycoupled thereto. Extending between end portions 192 a, 192 b is acentral portion 194 including a plurality of blocks or wedges, such asside blocks 200 and end blocks 202, surrounded by a cover, sleeve orretaining member (not shown) which functions to hold the blocks infrictional engagement with each other. A core member or rod 196 extendscentrally through end portions 192 a, 192 b and central portion 194where end blocks 202 are coaxially positioned on core 196 and areslidably translatable thereon. Core member 196 or a portion thereof maybe provided integrated with spacer 190 or may be provided as adetachable component of the device used to deliver and implant thespacer.

As with the previously described spacer, end portions 192 a, 192 b maybe made of a polymer based material or any other material which allowsfor simultaneous axial shortening and radial expansion when compressed.Blocks 200, 202 have a more rigid configuration in order to distract theadjacent spinous processes which define the interspinous space intowhich spacer 190 is positioned without substantial compression ofcentral portion 194. As such, the blocks may be made of a rigid polymermaterial, a metal, or the like. In order to effect radial expansion andaxial shortening of central portion 194, the blocks are selectivelysized, shaped and arranged such that an inwardly compressive force onend blocks 202 along the longitudinal axis of the spacer forces endblocks 202 together which in turn forces side or lateral blocks 200outward and away from each other, as illustrated in FIG. 22B. Theinwardly tapered sides of the blocks enable slidable engagement betweenadjacent blocks. The covering (not shown) around the blocks is made of astretchable material so as to accommodate the radial expansion ofcentral portion 194. As such, the cover may be made of a polymer basedmaterial.

When in an undeployed state, as shown in FIG. 22A, the central and endportions of spacer 190 have tubular or cylindrical configurations, andmay have any cross-sectional shape, length and or diameter as providedabove with respect to spacer 160 of FIGS. 18A and 18B. Deployment ofspacer 190 within an interspinous space may be accomplished in themanner described above. In a fully deployed state, as illustrated inFIG. 22C, spacer 190 has a dumbbell or H-shaped configuration with achange in length and height dimensions as provided above. The increaseddiameter of central portion 194 when spacer 190 is the deployedconfiguration distracts the adjacent vertebrae so as to provide painrelief. While the respective dimensions of the spacers change from anundeployed to a deployed state, the spacers may be configured such thatthe overall size of volume occupied by the spacer does not change.

Another interspinous spacer 210 of the present invention is illustratedin an undeployed/unexpanded state, in an intermediate state duringdeployment and in a deployed/expanded state in FIGS. 23A-23C,respectively. Spacer 210 includes expandable end portions 212 a, 212 bcapped by hubs 224 a, 224 b, respectively. As mentioned previously, oneor both hubs may be provided fixed to the end members or may bereleasably coupled thereto. Extending between end portions 212 a, 212 bis a central portion 214 including a plurality of linkages 216 andblocks 220, 222, which collectively provide opposing struts. Eachlinkage 216 has a length and is pivotally coupled to a side block 220and an end block 222, where end blocks 222 are coaxially positioned oncore 218 and are slidably translatable thereon. While the materials andconfiguration of end portions 212 a, 212 b may be as described above,linkages 216 are preferably made of a metal material. A core member orrod 218 extends centrally through end portions 212 a, 212 b and centralportion 214. Core member 218 or a portion thereof may be providedintegrated with spacer 210 or may be provided as a detachable componentof the device used to deliver and implant the spacer.

In an undeployed state, as shown in FIG. 23A, the central and endportions of spacer 190 have tubular or cylindrical configurations, andmay have any cross-sectional shape, length and or diameter as providedabove. As such, side blocks 220 are close together and end blocks 222are spaced apart with the lengths of linkages 216 aligned with thelongitudinal axis of core member 218. When opposing, inwardlycompressive forces are exerted on spacer 210 along its longitudinalaxis, end portions 212 a, 212 b axially compress and radially expand asdescribed above thereby forcing end blocks 222 together which in turnforce side or lateral blocks 220 outward and away from each other, asillustrated in FIG. 23B. This action causes linkages 216 to spreadapart, as shown in FIG. 23B, and move to positions where their lengthsare transverse to the longitudinal axis of core 218, as illustrated inFIG. 23C.

Interspinous spacer 230 of FIGS. 24A-24C employs the linkage arrangementof the central portion of spacer 190 of FIGS. 23A-23C in both of its endportions 232 a, 232 b as well as its central portion 234. Specifically,end portions 232 a, 232 b employ linkages 236, which are longer thanlinkages 238 used for central portion 234, but which are arranged insimilar engagement with side blocks 248 and end blocks 250. On each sideof central portion 234 and in between the central portion and the endportions 232 a, 232 b, respectively, are dampening washers 244. A coremember 240 extends between and through the end blocks 250 of distal endmember 232 a and the end blocks 252 of central portion 234 as well asthe dampening washers 244 positioned therebetween, all of which, exceptthe most distal end block, may slidably translatable along core member240. Core member 240 is releasably attached at a proximal end toratcheted drive rod 242 of a delivery device as discussed above withrespect to FIGS. 19-21 which rod 242 extends through the proximal endportion 232 a and hub 246, as illustrated in FIG. 24B.

In an undeployed state, as shown in FIG. 24A, the central and endportions of spacer 230 have tubular or cylindrical configurations. Assuch, side blocks 248 and 252 of end portions 232 a, 232 b and centralportion 234, respectively, are close together and end blocks 250 and 252of end portions 232 a, 232 b and central portion 234, respectively, arespaced apart with the lengths of linkages 236, 238 aligned with thelongitudinal axis of core member 240. When opposing, inwardlycompressive forces are exerted on the distal block 250 and hub 246 ofspacer 230 along its longitudinal axis, the end blocks are drawntogether thereby forcing side or lateral blocks 220 outward and awayfrom each other, as illustrated in FIG. 24B. This action causes thelinkages of the end and central portions to spread apart, and move topositions where their lengths are transverse to the longitudinal axis ofcore 240, as illustrated in FIG. 24C, the fully deployed state of spacer230.

The end portions and central portions of the compressible spacersdescribed above may be used in any combination. For example, thepolymer-based central portion of FIGS. 18A and 18B and the linkage endportions of FIGS. 24A-24C may be used together to form a spacer of thepresent invention. Such a spacer 260 is illustrated in FIGS. 25A-25C.Spacer 260 includes linkage-block end portions 262 a, 262 b and acompressible central member 264 around which is positioned acircumferential retaining member 278 made of a braided mesh-likematerial. A core member 274 extends between and through the end blocks270 of distal end member 262 a and through central portion 264, all ofwhich, except the most distal end block, may slidably translatable alongcore member 260. Core member 260 is releasably attached at a proximalend to ratcheted drive rod 272 of a delivery device as discussed abovewith respect to FIGS. 19-21 which rod 272 extends through the proximalend portion 262 a and hub 272, as illustrated in FIG. 25B.

In an undeployed state, as shown in FIG. 25A, the central and endportions of spacer 230 have tubular or cylindrical configurations. Assuch, side blocks 268 of end portions 262 a, 262 b are close togetherand end blocks 270 of end portions 262 a, 262 b are spaced apart withthe lengths of linkages 266 aligned with the longitudinal axis of coremember 274. When opposing, inwardly compressive forces are exerted onthe distal block 270 and hub 272 of spacer 260 along its longitudinalaxis, the end blocks are drawn together thereby causing linkages 266 ofthe end portions to spread apart thereby forcing side or lateral blocks268 outward and away from each other, as illustrated in FIG. 25B, untillinkages 266 move to positions where their lengths are transverse to thelongitudinal axis of core 274, as illustrated in FIG. 25C, the fullydeployed state of spacer 260.

Each of the expandable and or inflatable interspinous spacers describedthus far is particularly configured to be delivered minimallyinvasively, even percutaneously, from a single incision locatedlaterally to one side (left or right) of the spinal motion segment to betreated. However, the present invention also includes interspinousspacers which are deliverable through a mid-line incision made directlyinto the interspinous ligament. Examples of such spacers are nowdescribed.

FIGS. 26A and 26B are perspective and front views, respectively, ofinterspinous spacer 280 which is configured for implantation by way of apercutaneous mid-line approach. Spacer 280, shown in a deployed state,includes a central member or portion 282 and four struts or legs 284which are substantially radially expandable from central portion 282.Central portion 282 has a cylindrical configuration having a diametersized for delivery through a small gauge cannula and a length thatallows placement within an interspinous space. A lumen 285 extends atleast partially through the center of central portion 282 and isconfigured, e.g., threaded, to be releasably engaged to a delivery tool.

Each strut 284 includes one or more blocks 288. Where more than oneblock 288 per strut is employed, such as with spacer 280 which employstwo blocks 288 per strut 284 and spacer 290 of FIG. 27 which employsthree blocks 288 per strut 284, the blocks are stacked and slidablyinterconnected to each other in a manner that allows the to translatelinearly relative to each other along parallel axes. A tongue and grooveconfiguration 292 is employed with the illustrated embodiment tointerconnect stacked blocks, but any suitable interconnection whichenables such relative motion between the blocks may be used. Suchconfiguration may also be employed to interconnect the innermost blockto central member 282 where outer ridges or tongues 296 on centralmember 282 slidably interface with a corresponding groove on inner endof the innermost block. As such, blocks 288 are slidable relative tocentral member 282 along an axis parallel to the longitudinal axis ofcentral member 282. Depending on the application and the particularanatomy of the implant site, struts 284 may be evenly spaced apart aboutthe circumference of central member 282. In other embodiments thedistance between superior struts 284 a and between inferior struts 284 bmay vary and/or the distance between each of those and between struts onthe same side of the central member may vary.

Spanning between each strut pair 284 a and 284 b is a strap 286 a and286 b, respectively, affixed to the outermost blocks. Straps 286 may bemade of any suitable material which is strong enough to maintaindistraction between adjacent spinous processes and to endure anyfrictional wear which it may undergo due to natural spinal motion. Thestraps may be flexible such that they act as slings, or may beconformable to the spinous processes once in situ. Alternatively, thestraps may be non-conforming and rigid with a planar or curved shapedepending on the application at hand. Suitable strap materials includebut are not limited to polyester, polyethylene, etc.

With reference to FIGS. 28A-28E, various steps of a method according tothe present invention for implanting spacer 280 as well as other spacersof the present invention configured for a mid-line implantation approachinto a target spinal motion segment (defined by components of vertebralbodies 2 and 4) of a patient are described.

The initial steps of creating a percutaneous puncture and subsequentpenetration into the skin 30 and the dissection of the spinous ligament54 involve many of the same instruments (e.g., K-wire, trocar, cuttinginstrument, delivery cannula, etc.) and surgical techniques used in theipsolateral implantation approach described above with respect to FIGS.5 and 6. Upon creating an opening within the interspinous spaceextending between the superior spinous process 18 and the inferiorspinous process 22, a delivery instrument 300 having interspinous device280 operatively preloaded in an undeployed state at a distal end isdelivered to within the interspinous space. The delivery instrument 300is provided with a mechanism for releasably connecting to spacer 380,such as by way of threaded screw 302 (see FIG. 28D) which is threadedlyengaged with threaded lumens 285 of spacer 280.

As best illustrated in FIGS. 28A′ and 28A″, when in an undeployed state,spacer 280 has a relatively low profile to facilitate entry into theinterspinous space. Once properly positioned within the interspinousspace, deployment of the spacer 280 is initiated, as illustrated in FIG.28B, by manipulation of instrument 300 which simultaneously causesoutward radial movement of the outermost blocks of strut pairs 284 a,284 b and distal linear advancement of the proximal portion 304 ofspacer 282 (see FIGS. 28B′ and 28B″) resulting in radial expansion andaxial shortening of spacer 280. Spacer 280 may be configured such thatdeployment of the struts is accomplished by either or both axialrotation of internally componentry or axial compression of centralmember 282.

As the struts are radially extended, straps 286 a and 286 b emerge andthey become tauter as the slack in them is gradually reduced by theextension of the struts. Continued deployment of spacer 280 causesstraps 286 a, 286 b to engage with opposing surfaces of spinousprocesses 18 and 22. The radial extension of the struts is continued, asillustrated in FIGS. 28C, 28C′ and 28C″, until the desired amount ofdistraction between the vertebra is achieved. This selective distractionof the spinous processes also results in distraction of the vertebralbodies 2, 4 which in turn allows the disk, if bulging or distended, toretract to a more natural position. The extent of distraction orlordosis undergone by the subject vertebrae can be monitored byobserving the spacer under fluoroscopy.

At this point, the delivery instrument 300 is released from spacer 280by unscrewing threaded screw 302 from threaded lumen 285 and removing itfrom the implant site, as illustrated in FIG. 28D. Spacer 280 remainsbehind within the interspinous space, locked in a deployed state (seeFIG. 28E).

Spacer 280 may configured such that the struts are not retractablewithout active manipulation of delivery instrument 300 to ensure thattheir extension, and thus the distraction on the spinal motion segment,is maintained. As configured, spacer 280 may be easily repositioned orremoved by subsequent insertion of instrument 300 into the interspinousspace and operative engagement with the spacer. Instrument 300 is thenmanipulated to cause retraction of the struts and the straps, reducingthe spacer's profile to allow repositioning or removal of the spacer.

FIGS. 29A-29D illustrate another spacer 310 of the present inventionthat is implantable through a mid-line approach to the interspinousspace. Spacer 310 includes centrally opposed front and rear structuresor blocks 312 a, 32 b which are pivotally interconnected on both sidesto pairs of elongated linkages 314. The other end of each linkage 314 ispivotally connected to a lateral structure 318 a or 318 b. The resultingconfiguration provides interconnected strut pairs on each side of spacer310 which move and function similarly to the linkages described abovewith respect to the spacers illustrated in FIGS. 23, 24 and 25, i.e.,the lengths of linkages 314 extend parallel to the central axis ofspacer 310 when in a fully undeployed state (FIG. 29A) and extendtransverse to the central axis of spacer 310 in a fully deployed state(FIG. 29D). Extending between opposing superior lateral structures 318 aand between opposing inferior structures 318 b are straps 316 a and 316b, respectively.

Spacer 310 is implantable and deployable by way of a mid-line approachsimilar to that described above with respect to the spacer of FIGS.28A-28E. Spacer 310 is preloaded to a delivery instrument shaft 320which is insertable and axial translatable through a central openingwithin front block 312 a. The distal end of shaft 320 is releasablyattached to an axial member (not shown) of spacer 310. Axial member isfixed to rear block 312 b and extends along the central axis of spacer310, having a length which extends to front block 312 a when spacer 210is in a fully deployed state, as illustrated in FIG. 29D but whichextends only a portion of the length of spacer 310 when it is in anundeployed state (FIG. 29A) or a partially undeployed (FIGS. 29B and29C) state.

After the necessary space is created within the interspinous space asdescribed above, spacer 310, which is releasably connected to deliveryshaft 320 as described above, is inserted into the space in a fullyundeployed sate (see FIGS. 29A and 29A′). Deployment of the spacer isaccomplished by proximally pulling on shaft 320 which compresses rearblock 312 b towards front block 312 a. This in turn causes the linkages314 to pivot about their respective attachment points with superior andinferior lateral structures or blocks 318 a and 318 b forced away fromeach other, as illustrated in FIGS. 29B and 29B′. Continued pulling ofinstrument 320 further expands linkages 314 in a direction transverse tothe central axis of spacer 310 and extend straps 316 a, 316 b towardsrespective surfaces of the spinous processes. As front and rear blocks312 a and 312 b are centrally tapered, defining a bowtie or hourglassconfiguration, the strut pairs define a centrally tapered profile as thealign to their fully deployed position, as best shown in FIGS. 29C′ and29D′. In the fully deployed state, the spacer's axial member ispositioned within the opening of front block 312 a and locked to it.Additionally, straps 316 a and 316 b are firmly engaged against thespinous processes and the contacted vertebra are distracted from eachother. Delivery instrument 320 may then be released from spacer 310 andremoved from the implant site.

FIGS. 30A-30C illustrate yet another spacer 330 of the present inventionthat is implantable through a mid-line approach to the interspinousspace. As best illustrated in FIGS. 30A and 30A′, spacer 330 includes anelongated central member 332 extending between front and rear hubs 334 aand 334 b and a plurality of flexible or deformable struts 336 whichalso extend between hubs 334 a, 334 b. Struts 336 are configured to bedeformable and to have a directional character to facilitate deploymentof them radially outward from central member 332. Examples of suitableconstructs of these struts include but are not limited to thin metalplates, e.g., flat springs, wire bundles or a polymer material.Extending between and affixed to each of strut pairs 336 a and 336 b arestraps 338 a and 338 b, respectively.

The proximal end 342 of central member 332 is provided with ratchetedgrooves which are releasably engaged within the distal end of 352 ofdelivery instrument 350 (see FIG. 30C′). Front hub 334 a is providedwith an opening 340 which also has a grooved internal surface forengaging with the grooves of central member 332.

Spacer 330 is implantable and deployable by way of a mid-line approachsimilar to that described above with respect to the spacer of FIGS.29A-2D. Spacer 330 is preloaded in a fully undeployed state to deliveryinstrument shaft 350 as illustrated in FIGS. 30B and 30B′. After thenecessary space is created within the interspinous space as describedabove, spacer 330 is inserted into the interspinous space. Deployment ofthe spacer is accomplished by proximally pulling on shaft 350, byratcheting as described above, which compresses rear hub 334 b towardsfront hub 334 a or distally pushing on front hub 334 a towards rear hub334 b. This in turn causes struts 336 a, 336 b to flex or bend outward,as illustrated in FIGS. 30C and 30C′. Continued pulling of instrument350 (or pushing of hub 334 a) further bends the struts such that theydefine an X-shaped structure with straps 338 a and 338 b forcablyabutting against the interspinous processes. The pulling (or pushing)action advances the grooved proximal end 342 of central member 332 intogrooved opening 340 of front hub 334 a. The opposing grooves of thecentral member and the opening provide a ratchet relationship betweenthe two whereby central member is readily translatable in a proximaldirection but not in a distal direction, thereby locking spacer 330 in adeployed state. Upon achieving the desired amount of distraction betweenthe vertebra, delivery instrument 350 is released from spacer 310 (suchas by unscrewing) and removed from the implant site.

The subject devices and systems may be provided in the form of a kitwhich includes at least one interspinous device of the presentinvention. A plurality of such devices may be provided where the deviceshave the same or varying sizes and shapes and are made of the same orvarying materials. The kits may further include instruments and toolsfor implanting the subject devices, including but not limited to, acannula, a trocar, a scope, a device delivery/inflation/expansion lumen,a cutting instrument, a screw driver, etc., as well as a selection ofscrews or other devices for anchoring the spacer tabs to the spinousprocesses. The kits may also include a supply of the expandable bodyinflation and/or expansion medium. Instructions for implanting theinterspinous spacers and using the above-described instrumentation mayalso be provided with the kits.

The preceding merely illustrates the principles of the invention. Itwill be appreciated that those skilled in the art will be able to devisevarious arrangements which, although not explicitly described or shownherein, embody the principles of the invention and are included withinits spirit and scope. Furthermore, all examples and conditional languagerecited herein are principally intended to aid the reader inunderstanding the principles of the invention and the conceptscontributed by the inventors to furthering the art, and are to beconstrued as being without limitation to such specifically recitedexamples and conditions. Moreover, all statements herein recitingprinciples, aspects, and embodiments of the invention as well asspecific examples thereof, are intended to encompass both structural andfunctional equivalents thereof. Additionally, it is intended that suchequivalents include both currently known equivalents and equivalentsdeveloped in the future, i.e., any elements developed that perform thesame function, regardless of structure. The scope of the presentinvention, therefore, is not intended to be limited to the exemplaryembodiments shown and described herein. Rather, the scope and spirit ofpresent invention is embodied by the appended claims.

1. A method for stabilizing a superior vertebra having a superiorspinous process relative to an inferior vertebra having an inferiorspinous process, wherein the superior and inferior spinous processesdefine an interspinous space, the method comprising: inserting aninterspinous device into the interspinous space by moving theinterspinous device anteriorly substantially along a midline relative tothe superior and inferior spinous processes through an incision locatedposterior of the interspinous space; moving a superior strut unit of theinterspinous device by radial expansion to extend superiorly such thatthe superior spinous process is seated between first and second superiorstruts of the superior strut unit, wherein the superior strut unit ismoved after implanting the interspinous device; and moving an inferiorstrut unit of the interspinous device by radial expansion to extendinferiorly such that the inferior spinous process is seated betweenfirst and second inferior struts of the inferior strut unit, wherein theinferior strut unit is moved after implanting the interspinous device.2. The method of claim 1, wherein the interspinous device has ananterior-posterior axis and the superior and inferior struts extendalong the anterior-posterior axis while inserting the interspinousdevice into the interspinous space.
 3. The method of claim 2 whereinmoving the superior and inferior strut units comprises extending thefirst and second superior struts and the first and second inferiorstruts away from the anterior-posterior axis.
 4. The method of claim 3wherein the interspinous device has a tool interface facing posteriorlyand the method comprises engaging a delivery tool with the toolinterface before inserting the interspinous device into the interspinousspace, and wherein extending the first and second superior struts andthe first and second inferior struts comprises manipulating the deliverytool while the delivery tool extends posteriorly relative to the firstand second vertebrae through the incision posterior of the interspinousspace.
 5. The method of claim 4 wherein the first and second superiorstruts and the first and second inferior struts are extendedsimultaneously.
 6. The method of claim 2 wherein the first and secondsuperior struts and the first and second inferior struts are rotatedaway from the anterior-posterior axis simultaneously.
 7. The method ofclaim 4 wherein, while the delivery tool extends through the incision,the delivery tool has a shaft extending substantially perpendicular to aplane that is substantially perpendicular to the anterior-posterioraxis.
 8. The method of claim 1 wherein moving the first strut unit andmoving the second strut unit comprises rotating the first and secondstrut units such that the first and second superior struts and the firstand second inferior struts are in a transverse plane at leastsubstantially perpendicular to the anterior-posterior axis afterextension.
 9. The method of claim 8 wherein the superior strut unit andthe inferior strut unit together define an X-shaped configuration in thetransverse plane after deployment.
 10. The method of claim 8 wherein thesuperior strut unit and the inferior strut unit together define anH-shaped configuration in the transverse plane after deployment.
 11. Themethod of claim 1, further comprising forming the incision at themidline posterior of the interspinous space and inserting the devicecomprises passing the device through the midline incision.
 12. A methodfor stabilizing a superior vertebra having a superior spinous processrelative to an inferior vertebra having an inferior spinous process,comprising: creating an incision at a midline located posterior of theinterspinous space; inserting an interspinous device into theinterspinous space by moving the interspinous device anteriorly relativeto the incision; and changing the interspinous device from an undeployedconfiguration to a deployed configuration by radial expansion, whereinthe interspinous device includes a pair of inferior struts and a pair ofsuperior struts which are configured to have a low profile in theundeployed configuration relative to the deployed configuration, andwherein the inferior struts of the interspinous device are configured toseat the inferior spinous processes in the deployed configuration andthe superior struts of the interspinous device are configured to seatthe superior spinous processes in the deployed configuration, andthereby relieve pain.
 13. The method of claim 12, wherein theinterspinous device has an anterior-posterior axis and the superior andinferior struts extend along the anterior-posterior axis while insertingthe interspinous device into the interspinous space.
 14. The method ofclaim 13 wherein the interspinous device has a tool interface facingposteriorly and the method comprises engaging a delivery tool with thetool interface before inserting the interspinous device into theinterspinous space, and wherein extending the first and second superiorstruts and the first and second inferior struts comprises manipulatingthe delivery tool while the delivery tool extends posteriorly relativeto the first and second vertebrae through the incision posterior of theinterspinous space.
 15. The method of claim 12 wherein moving thesuperior and inferior strut pairs comprises extending the first andsecond superior struts and the first and second inferior struts awayfrom the anterior-posterior axis.
 16. The method of claim 15 wherein thefirst and second superior struts and the first and second inferiorstruts are extended simultaneously.
 17. The method of claim 15 wherein,while the delivery tool extends through the incision, the delivery toolhas a shaft extending substantially perpendicular to a plane that issubstantially perpendicular to the anterior-posterior axis.
 18. Themethod of claim 12 wherein the first and second superior struts and thefirst and second inferior struts are rotated away from theanterior-posterior axis simultaneously.
 19. The method of claim 12wherein moving the inferior strut pair and moving the superior strutpair comprises rotating the inferior and superior strut pair such thatthe first and second superior struts and the first and second inferiorstruts are in a transverse plane at least substantially perpendicular tothe anterior-posterior axis after extension.
 20. The method of claim 19wherein the superior strut pair and the inferior strut pair togetherdefine an X-shaped configuration in the transverse plane afterdeployment.
 21. The method of claim 19 wherein the superior strut unitand the inferior strut unit together define an H-shaped configuration inthe transverse plane after deployment.
 22. The method of claim 12,further comprising forming the incision at the midline posterior of theinterspinous space and inserting the device comprises passing the devicethrough the midline incision.